SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

3. DEVELOPING RIVER WATER BODY ENVIRONMENTAL STANDARDS

3.1 Defining indices of hydrological alteration

Stage 1 of the project reviewed environmental standards and parameters included a literature review to identify the full range of parameters for both rivers and lakes that may need to be controlled and the circumstances in which they are significant. In tandem with this work, a review and appraisal of existing standards, both within the UK and internationally was carried out to determine where there are any gaps – i.e. any parameters that have been identified as relevant but for which there are no existing UK or international standards available.

The results of Stage 1 were presented in a report, whose main conclusions were:

• Most countries have various methods of determining environmental flows, each defined for a different purpose, e.g. scoping or impact assessment. • Licensing of reservoir releases and abstractions present quite different problems, and different methods have been developed to deal with these issues. With reservoir releases, the flow regime is likely to be subject to significant management (apart from very large floods that by-pass the dam), since it needs to be created. Abstractions, by and large, have no impact on high flows and so the focus is on low flow impacts. • Where data are scarce, expert opinion is used, and increasingly a formal structured approach to getting consensus amongst a group of experts, including academics and practitioners, is favoured. • There is wide acceptance that all parts of the flow regime have some ecological importance. As a result, there is a growing move away from single low flow indices towards environmental flows. • Many methods determine environmental flows in relation to the natural flow regime of the river. Some methods define flow in terms of site characteristics, such as flow per unit width needed for salmon migration in Lancashire, but it has not been possible to examine the data or the basis of these derivations. Other methods define environmental requirements in terms of more direct hydromorphological elements, such as water depth and velocity. • Small scale studies have shown that flow interacts with morphology to define physical habitat (such as width, depth, velocity and substrate) for specific organisms. These quality elements vary spatially; water is deep in pools and shallow on riffles; velocity is high in riffles and low in pools. Standards based on these quality elements at the broad water body scale cannot be readily defined. To implement standards at the reach scale, site data are essential. • Implementation of the WFD will require that environmental standards are applied for all water bodies regardless of hydrological and ecological data available. Consequently, standards are required that can be applied without having to visit the water body or collect excessive data. This means that standards must be related to parameters that can be obtained from maps or digital databases, such as river flow, catchment area or geology. Any resulting standards will have less predictive power at a local scale and cannot be tested using site data. • A hierarchical approach may be needed in which a broad scale approach, perhaps based on flow, is used as a screening tool to assess all water bodies. A more detailed approach, perhaps based on depth or velocity, may be applied to a smaller number of sites identified as requiring close attention. • The natural flow regime is complex and is characterised by timing, magnitude, duration and frequency; all of which are important for different aspects of the river ecosystem. To produce operational standards, there is a need to identify a

38 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

small number of parameters that capture its most significant characteristics. For example the number of high flow events greater than three times the median flow has been shown to be related to the structure of macrophyte and macro- invertebrate communities in New Zealand (Clausen, 1997).

The main outcome of Stage 1 was that the regulatory parameter for environmental standards for rivers at a broad scale should be flow, since data on potentially more ecological meaningful parameters, such as depth and velocity are not widely monitored and cannot be determined without detailed surveys at all sites. Since flow varies greatly between water bodies, generic flow standards need to be expressed in dimensionless terms, such as proportions of natural flow or unit flow per drainage area or channel width. Nevertheless, UK agencies should develop a hierarchical approach to standards, where broad scale methods based on flow are used for screening, but detailed scale methods based on more directly ecologically meaningful parameters, such as depth and velocity, are used for site level impact assessment and license setting.

The flow regime of a river or level regime of a lake is often a complex time-series, rising and falling in response to precipitation, snowmelt, geology and catchment conditions. Many of the methods used around the world to set environmental standards for water resources are based on the premise that freshwater aquatic ecosystems are adapted to natural variations in the hydrological regime and are thus dependent upon them. For example, the Building Block Methodology (BBM) developed in South Africa (Tharme and King, 1998; King et al. 2000) recognises that river ecosystems are reliant on basic elements (building blocks) of the flow regime, including low flows (that provide a minimum habitat for species, and prevent invasive species), medium flows (that sort river sediments, and stimulate fish migration and spawning) and floods (that maintain channel structure and allow movement onto floodplain habitats). Richter et al (1996) analysed the magnitude (of both high and low flows), timing (indexed by monthly statistics), frequency (number of events), duration (indexed by moving average minima and maxima) and rate of change of natural flow regimes. They defined 32 parameters that were considered to be relevant to the river ecosystem. This was reduced to 8 key parameters in a redundancy analysis (Poff et al., 2000) as many of the 32 original indices were inter- correlated. Richter et al further suggested that initial flow management targets could be that all parameters should be within 1 standard deviation from the natural mean. The method has been adapted for analysis of Scottish rivers by Black et al (2000). However, precise ecological relevance of these parameters has not been defined and the 1 standard deviation threshold has never been tested.

Alterations to the hydrological regime due to abstractions, impoundments, diversions and river basin transfers can have very diverse impacts on any of these indices depending on their type, infrastructure and operation. To make the process of defining environmental standards for water resources manageable, it is necessary to organise all the possible hydrological alterations into a few scenarios for which ecosystem impacts can be analysed. The simplest approach is to consider two scenarios of hydrological alteration: (1) abstraction (directly from the river or aquifer supplying the river) and (2) impoundment where abstracted water is taken from a reservoir.

(1) Abstraction Abstraction licenses may be complex, allowing different volumes to be taken at different times and according to different hydrological conditions. However, we will consider only a constant abstraction of a fixed volume of water, which will reduce the entire regime. Figure 20 shows a natural river regime (in blue) and the regime for the

39 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 same period given a constant abstraction of 0.06 m3s-1. It is evident that the abstraction is having a greater proportional impact at low flows; it is having no impact on timing of floods and very little impact on their magnitude. Because of this, the focus of environmental standards to manage abstractions is on low flows.

1.800

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0.000 01/01/1986 20/02/1986 11/04/1986 31/05/1986 20/07/1986 08/09/1986 28/10/1986 17/12/1986 date

Figure 20 River flow regimes: natural (blue) and impacted by a constant abstraction of 0.06 m3s-1 (pink)

(2) Impoundment Impoundments can have even more complex impacts on the hydrological regime than abstractions depending on the size of the weir or dam, settings of sluice gates or release structures, level and size of spillways and dam operation. However, to make the exercise manageable we will consider a single impoundment scenario. Figure 21 shows the same natural flow regime (in blue) as Figure 20 and the regime for the same period with an impoundment in place. In this case, there is a constant compensation flow release from the dam of 0.13 m3s-1. It can be seen that in the late summer/early autumn the compensation flow is greater than the natural flow. Major floods in February, April and December pass the dam via the spillway. However, small floods in late Spring, Summer and Autumn disappear from the hydrograph as water is stored in the reservoir.

40 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

1.800

1.600

1.400

1.200

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flow 0.800

0.600

0.400

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0.000 01/01/1986 20/02/1986 11/04/1986 31/05/1986 20/07/1986 08/09/1986 28/10/1986 17/12/1986 date

Figure 21 River flow regimes: natural (blue) and impacted by an impoundment with a constant compensation flow of 0.13 m3s-1 (pink)

The two scenarios require different types of management: restrictive and active (Acreman and Dunbar, 2004). Abstraction needs restrictive management, in which environmental protection is achieved by restriction of practices by, for example, a “hands-off” flow (HOF) (Barker & Kirmond, 1998) where abstraction is permitted provided that the flow is above a certain critical value, but must reduce or cease when the flow falls below this value. The flow may continue to fall, but this will be at a natural rate governed by meteorological and geological conditions, not due to artificial influences. Reservoir control requires “active management” in which environmental protection is achieved by actively making releases from a reservoir.

Different levels of (compensation) flow releases could be made at various times of the year and for many dams (depending on the release gate structure) freshet or flood releases can be made such the various ecologically important elements of the flow regime can be generated (e.g. low flows in summer, higher flows in winter, spates in autumn) as in the Building Block Methodology.

It is recognised that the two scenarios do not include the operation of dams for hydro-power generation. This can have significant impacts on the hydrological regime of the river and its downstream ecosystem. In particular, the flow downstream of hydro-power dams reflects power demand, exhibiting very high rates of change over time; with sudden massive increases and decreases as turbines are turned on and off. There is currently insufficient knowledge on critical rates of change of flow to set generic standards on hydro-power operations.

3.2 Good Ecological Status or Good Ecological Potential

The Water Framework Directive requires member states to achieve good ecological status (GES) in all surface and ground waters. GES is defined qualitatively as slight

41 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 deviation from the reference status, based on populations and communities of fish, macro-invertebrates, macrophytes and phytobenthos, and phytoplankton. Exceptions to the Directive are permitted for water bodies that are designated as heavily modified water bodies (HMWB). Most effort in identifying and designating HMWBs has focused on physical alterations to water bodies, such as dams, bridges, weirs and concrete embankments (Dunbar et al, 2002). For such water bodies, the aim is to achieve good ecological potential (GEP); a lower status than GES. HMWBs are beyond the scope of this project, so environmental standards for water bodies containing dams are not required. However, the impacts of a dam can be felt in water bodies some way downstream (often until the next significant tributary inflow) that are not themselves designated as HMWBs. These impacts may be in terms of flow regime or water quality. Work for the World Commission on Dams (Acreman et al., 2000) identified a range of ecological impacts of dams including altered flow regime, reduced sediment load, reduced temperature and presence of chemical produced by stratification of water in the reservoir, such as hydrogen cyanide.

The Common Implementation Strategy for the WFD, Guidance note 4 "Identification and Designation of Heavily Modified and Artificial Water Bodies” states that “… substantial hydrological changes that are accompanied by subsequent non- substantial morphological changes would be sufficient to consider the water body for a provisional identification as HMWB." Furthermore, even if a water body is eventually designated as a HMWB, the flow regime to achieve GES is required as a part of the designation process.

It is important therefore to consider whether GES can be achieved by both restrictive and active management and whether their environmental standards must be identical. As stated abstractions reduce the entire flow regime but maintain natural variability, which is an ecologically important characteristic. In theory a dam could be operated such that its flow releases mimic natural patterns, although this would need a complex system that linked the flow signal in an unregulated reference catchment to the operations of the sluice gate which would need to be altered perhaps daily, called a translucent dam. In practice this would be difficult to achieve. A more realistic question is whether GES can be achieved by less frequent alterations to the gates settings through, for example, a building block approach (Figure 22); dispensing with short term natural variability. A major problem is that if the water body is heavily modified, even a natural flow may not achieve GES. For example, a dam may trap sediment and releasing naturally high flows below the dam may cause major erosion. Likewise naturally high flows in a concrete lined straight channel may create velocities beyond the swimming speed of fish which would be detrimental if sufficient refugia were not available. In such cases, the best that can be achieved is GEP; i.e. the flow regime that gives the ecological status given the limitation of other quality elements. Achieving GES may not be possible.

This issue is addressed below.

42 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 discharge

J F M A M J J A S O N D

Figure 22 The Building Block Approach. The blue line shows one year of a natural regime for a catchment. The green line shows a flow release pattern from a reservoir that maintains some key elements of the flow regime (low flows in summer, higher flows in winter

3.3 Defining expert-based standards

To define the standards, a workshop was held in Edinburgh on 8 April 2005 at which experts on macrophytes, macro-invertebrates and fish were present, plus more general experts in river and lake management from Environment Agency of England and Wales, Scottish Environment Protection Agency and Environment and Heritage Service Northern Ireland. The workshop report is attached as Annex 1. The fish experts requested a subsequent meeting, which was held on 28 April 2005. The report of this meeting is given as Annex 2.

Workshop participants felt strongly that insufficient knowledge was available to define precise generic environmental standards. Instead their thinking was based on a precautionary approach by considering incrementally higher levels of flow alteration and deciding at what level of flow alteration we could no longer be certain that good status would be achieved.

A series of broad concepts emerged:

1. Standards derived from expert knowledge were the best available, but should be considered as first approximations. Wherever possible, local data and knowledge should be used to refine the standards. Major scheme might require an Environmental Impact Assessment. In most cases this would most likely lead to less stringent standards (i.e. allowing greater alteration of the hydrological regime), since the expert consensus reached at the workshops was precautionary.

2. Suitable conditions for river biota are controlled by many factors including water depth, flow velocity, temperature and light. River flow discharge is not a direct driving variable and only impacts indirectly through its interaction with channel geometry to create depth and velocity and through dilution effects. Ideally, environmental standards should be set on the basis of direct variables, but

43 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

insufficient data are available and these variables are not monitored widely or easy derivable. Broad standards can be set on the basis of flow discharge for river types in which channel geometry can be assume to be similar. Any follow- up detailed studies must consider the direct variables, such as depth and velocity, particularly in river water bodies where the channel geometry has been altered, for example by channel widening, deepening or construction of weirs or embankments.

3. In general standards are specified in terms of deviations from the natural flow regime. The reference natural flow regime considered would be the actual regime of the past 50 years or so, plus abstractions and minus discharges, or simulated from models such as Low Flows 2000. This would not account explicitly for changes in climate or land use. In exceptional circumstances the reference flow may be the gauged flow, for example where the flow has been augmented by major discharges for a long historical period, such as the River Don in Yorkshire.

4. With some variations, flow regimes should be within about 20% of natural to achieve GES. This is consistent with English Nature flow targets of 10% abstraction for rivers designated as Special Areas of Conservation (SACs) under the Habitats Directive which is broadly equivalent to high status.

5. In the restrictive management standards defined, there was wide support given for the idea of preserving Q95 flow by designating this as a “hands-off” flow. The concept being that when the river flow drops to and below Q95, abstraction either stops or is significantly reduced.

6. Explicit seasonal variations in standards may not be required if the abstraction levels are defined in terms of seasonal flow statistics; e.g. hands-off flow is Q95 for that season.

7. It is difficult to define environmental standards for a simple screening approach to active management that are different from those for restrictive management; i.e. standards for GES can not be defined for “normal” infrequent operation of sluice gates which did not reproduce natural daily fluctuations of river flow. Such seasonal alterations in compensation flow releases plus occasional freshets and floods could achieve GEP.

8. If restrictive management standards for GES are applied to impoundments, then they will fail. The implication of this is that further detailed studies will be required for all impoundments beyond the screening approach.

3.4 Macrophytes

Details of expert standards defined for macrophytes are given in the workshop report in Annex 1. The standards are summarised in Table 14 below.

The river water body types relate to the generic typology based on Holmes et al. (1998) shown in Table 2.

The standards have a potential inconsistency implementation in that abstracting 20% of flow when the flow is just above Q95 will reduce the flow below the HOF of Q95. In practice, abstraction will need to reduce gradually as the flow reaches HOF.

44 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

Table 14 Summary of expert standards defined for macrophytes

Restrictive (1) abstraction For autumn and winter periods for all rivers flow types, permissible abstraction levels are 20% of management total flow on the day. In spring/summer, for B2 and C1 types the critical level is also 20%; for other types critical level is 10%. HOF is Q95 in March – May period for all types. Active flow (2) floods For all river types floods events of 5-7 times the management median flow are important and need to be (GEP only - maintained at 20-30% of natural occurrence (e.g. see restrictive one day duration on small catchments). management (3) For all river types continuous flow releases need standards for compensation to be maintained at Q95. For types C2, D1 and GES) flow D2 it is important to ensure that the flow (of around Q95) fluctuates by + 100% / - 50% to maintain periodic inundation/drying of bryophytes.

3.5 Macro-invertebrates

Details of expert standards defined for macro-invertebrates are given in the workshop report in Annex 1. The standards are summarised in Table 15 below.

The river water body types relate to the generic typology based on Holmes et al. (1998) shown in Table 2.

Table 15 Summary of expert standards defined for macro-invertebrates

Restrictive (1) abstraction For all seasons permissible abstraction levels flow are the same. A2, B1, C2 and D2 types require management highest levels of protection with 10% permissible abstraction; A1 rivers require lowest level at 30%. For other types the critical level is 20%. HOF is seasonal Q97 for all river water body types. Active flow (2) floods For all periods flood requirements are the same. management Lowest protection needed for A1 (40%) and D2 (GEP only - (50%) of natural flooding regime. A2 and D1 see restrictive require highest protection at 80%. B1 and C2 management require 60%, B2 and C1 require 70% of natural standards for flooding regime. GES) (3) For all periods continuous flow releases are the compensation same. For good ecological status flows should flow be as (1) abstraction. For good ecological potential, highest requirements are for D2 rivers at Q60. For B1, B2, C1, C2 rivers, flow release should be Q70. For A2 and D1 Q80. Lowest requirements are for A1 rivers at Q90.

45 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

Modelling of the response of LIFE score to flow

The analysis in this section was undertaken by CEH as part of the EU Framework 6 project "REBECCA" (Relationships between the ecological and chemical status of surface waters), and is provided as a free contribution to project WFD48 in order to facilitate its dissemination.

In addition to the expert input to defining standards, analysis was undertaken of LIFE (Lotic Invertebrate index for Flow Evaluation) score data, calculated from according samples of macroinvertebrates according to the method of Extence et al ,1999. This analysis was based on a subset of the 290 sites collated for the Environment Agency LIFE GRC (Generalised Response Curves) project. This dataset only includes sites close to gauging stations which have not been subject to any chronic water quality problems. From this dataset, 29 sites were subsequently excluded for various reasons, principally that they had a habitat structure unsuitable for LIFE analysis, had intermittent water quality problems or had very low flow variability downstream of a reservoir. A further criterion was that there should be at least 5 autumn samples taken in the 14 year period of record (1990-2003). All these criteria together left 186 sites which were used in this analysis. This dataset has 1662 samplings, of which 1573 were lab sorted. Of the 186 sites, 144 are deemed broadly natural (following procedures undertaken in the CEH-Environment Agency Low Flows 2000 and generalised rainfall-runoff modelling projects) and 42 hydrologically impacted. Of the gauges linked to the 186 macroinvertebrate sampling sites, one is linked to 8 sites, three to 3 or 4 sites, 24 to 2 sites and the rest to 1 site.

A common set of catchment and site characteristics (hereafter termed environmental variables) was used in the analysis:

Variables calculated at gauge: • Base flow index • Mean flow for standard period (this effectively integrates catchment area and effective rainfall)

RIVPACS catchment variables (these can be calculated from GIS data, no missing values) • Altitude of site • Distance from source • Slope (strictly a site variable, but it can be calculated from GIS data so is included here)

RIVPACS site variables (collected when sample taken, some values missing) • Alkalinity • Substrate • Mean depth • Mean width

Plus Expected LIFE score (ELIFE) from RIVPACS, which is determined from the suite of environmental variables.

The common hypothesis in these analyses was whether the slope of response to LIFE score to flow varied in any systematic fashion with any of the environmental variables. If it did, then this would be evidence for differing sensitivity to flow for different catchment or site types, and thus for differing sensitivity to abstraction or flow regulation.

46 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

In each of the following sequence of analyses, LIFE score was expressed in two alternative ways, observed / expected (O/E), where expected score is calculated by RIVPACS, and the raw unstandardised score. Two different formulations for standardising flow variables were chosen: standardised flows (flow divided by mean flow for period of record) and normalised flows ((flow-mean flow)/standard deviation of flow). The latter approach standardises all flows to a common range while the former allows gauges with greater variability around the mean (ie flashier catchments) to retain this variability. In each case, the between site variation in LIFE score is modelled using a two level random effects approach with flows as a fixed effect and environmental variables varying by site, assuming that deviations of site mean scores from an overall mean score can be modelled with a normal distribution with a variance determined from the data. A mean score from each site can be calculated, this is called a BLUP or best linear unbiased predictor.

Analysis 1. univariate relationship between site LIFE score and environmental variables, excluding any flow variables.

Results for raw LIFE score: ELIFE shows a clear relationship as one might expect, virtually all other variables show the expected relationships although the relationship with distance from source is unclear.

Results for LIFE O/E: Here as one might expect the relationships are far less distinct (indicating that RIVPACS is doing its job). BFI shows a positive relationship with LIFE O/E, this has been observed in the LIFE GRC project and is perhaps not surprising as it is not a variable in RIVPACS. This is possibly indicating the under-prediction of RIVPACS ELIFE on baseflow-dominated catchments. Other variables show fairly indistinct relationships aside from slope (slight positive relationship) and substrate (slight negative relationship). These latter two possibly reflect the formulation of the LIFE score to reflect velocity and siltation preferences.

Table 16 Visual assessment of LIFE score relationships with environmental variables (no flow covariates)

Visual (non-statistical) assessment of relationship1 Variables calculated at gauge Base flow index -- Mean flow for standard period ++ RIVPACS catchment variables Altitude of site +++ Distance from source 0 Slope +++ RIVPACS site variables Alkalinity --- Substrate --- Mean depth -- Mean width + ELIFE +++

1 +++/--- very strong positive / negative; ++/-- strong or obvious; +/- weak, 0 no relationship

47 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

Analysis 2. Univariate relationships between raw and O/E LIFE and environmental variables, once within-site LIFE score is related to antecedent flow conditions

The antecedent flow conditions were indexed as the Q95 of all the flows in the six months before the sample was taken: this was chosen as it has been shown to be an important flow variable in previous analyses for the GRC project. Results are presented for the two methods of flow standardisation in Figure 23 and Table 17.

For intercept (i.e. overall mean LIFE score), the method of flow standardisation does not matter. However it does matter for slopes, flows standardised by mean flow give some positive relationships (Figure 23B), whereas normalised (z-score flows) give no clear relationships (Figure 23A). Note that in the case of comparing slopes, the intercept for the raw scores takes into account part of the “E”. Hence the slope graphs for O/E LIFE and raw LIFE look very similar, the results for O/E LIFE are not shown.

48 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

A B 0.0 2.5 0.0 2.5 0.05 0.05

0.2 0.6 1.0 -2 0 2 4 0.2 0.6 1.0 -2024

BFI log(meanSP) BFI log(meanSP) 0.0 2.5 0.0 2.5 0.05 0.05

0.0 0.3 0.6 0 100 200 0.0 0.3 0.6 0 100 200

Q95dMEAN ALT Q95dMEAN ALT 0.0 2.5 0.0 2.5 0.05 0.05

15 50 -1 1 3 15 50 -1 1 3

D_F_SOURCE log(SLOPE + 0.1) D F SOURCE log(SLOPE + 0.1) 0.0 2.5 0.0 2.5 0.05 0.05

0 150 300 -5 0 5 0 100 250 -5 0 5

PAlkalinity MSUBST PAlkalinity MSUBST 0.0 2.5 0.0 2.5 0.05 0.05

23456 02050 23456 02050

log(PDepth) AvgOfAVG WIDTH log(PDepth) AvgOfAVG WIDTH 0.05 0.0 2.5 6.5 7.5 6.5 7.5

ELIFE3 ELIFE3

Figure 23 Univariate relationships between slope of LIFE response to flow and site/catchment predictors. A: Flows normalised as z-scores. B. Flows standardised by mean flow. Y axis is slope per unit change in flow, in raw LIFE score units.

49 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

Table 17 Visual assessment of LIFE score relationships with environmental variables (one flow covariate): Results for raw LIFE scores

Intercept Slope Variables calculated at gauge Z score flows dMean flows Z score flows dMean flows Base flow index - - 0- --- Mean flow for standard period + + 0+ +++ RIVPACS catchment variables Altitude of site ++ ++ 0 + Distance from source 0 0 0 0 Slope ++ ++ 0+ + RIVPACS site variables Alkalinity -- -- 0- -- Substrate ------Mean depth ------Mean width + + + ++ ELIFE +++ +++ + +++

Analysis 3. Results of multiple regression of raw LIFE scores vs slopes of LIFE to flow (standardised by mean flow).

In the case of flows divided by mean flows, there were several potentially important variables in the graphical analysis. Hence, a stepwise multiple regression was used to try to reduce to a few key variables. The variables retained are summarised in Table 18. ELIFE effectively summarises the entire suite of RIVPACS environmental variables and is retained. Site slope (which is included as a RIVPACS predictor) is not retained as having any extra predictive capability. Of the variables not in RIVPACS, overall long-term mean flow and long-term Q95/mean flow are retained, whereas BFI is not. There is a positive relationship between mean flow and slope of LIFE response and a negative relationship between Q95dMEAN and slope of LIFE response.

Table 18 Retained variables from multiple regression and their standard errors

Estimate Std. t value Pr(>|t|) Error (Intercept) -2.0429 0.8031 -2.544 0.01186 4 log(meanSP) 0.102 0.0269 3.79 0.00020 9 Q95dMEAN -1.8103 0.3147 -5.753 4.03E-08 ELIFE3 0.5192 0.11314.591 8.57E-06

Overall Conclusions

In Analysis 3 the BFI term is not retained, but another index of flashiness (Q95/mean flow) is. It is perhaps more obvious that ELIFE3 together summarises the effects of all the RIVPACS environmental variables. To recap, we are interpreting sensitivity to flow as change in LIFE score for a unit change in flow.

Thus: • Sites with higher mean flow are more sensitive • Sites with higher ELIFE are more sensitive

50 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

• Sites with lower long term Q95/mean flow are more sensitive

These conclusions are for the case where flow is standardised between sites as a proportion of mean flow. This means that standardised flow will vary more for flashy rivers than for baseflow dominated rivers. Thus a unit change in flow is more significant in rivers whose Q95 is a lower proportion of the mean, in larger rivers, and sites with a higher expected LIFE score (i.e. generally more “upland” rivers.

However, when flows normalised as z-scores, i.e. the variability around the mean is standardised as well, none of the site-level explanatory variables are significant predictors. In effect the effects of the site-level hydrological predictor variables are removed.

Hence, if regulation is through licences based on a proportion of a low flow statistic like Q95, there is an inherent compensatory mechanism, and all rivers behave essentially the same. In other words, the characteristics used do not differentiate between the sensitivity to flow change of the sites. This does not mean differences in sensitivity exist.

There are several caveats to this analysis. Firstly, that the ranges of altitudes looked at is not large, there are few sites in the dataset over 200m. This is partly limited by the fact that there are far fewer gauging stations at higher altitudes, but also because the analysis is for England only. Data for Scotland are available, and sample sites are being screened against gauging stations, however they were not available at the time of this report. Secondly, the analyses are based on samples identified to family level, which is the main approach used by the Agency. Species level data may show clearer patterns, although there would be far fewer sites available for analysis.

3.6 Fish

Details of expert standards defined for fish are given in the workshop report in Annex 2. The standards are summarised in Table 19 below.

The 5 river water body types in Table 19 relate to fish community types define at the expert workshop based on information from Cowx et al. (2004). • Chalk stream communities • eurytopic/limnophilic – roach, bream, tench, pike, bleak • rheophilic cyprinids – dace, chub, adult resident trout • salmonids – adult salmon • salmonids – spawning and nursery areas

There is currently no precise method for defining which fish communities are expected in which river water bodies. Development of a method would need to be the subject of further study.

The definition of restrictive management standards for fish communities have been defined in a more complex way than for macrophytes and invertebrates to avoid the inconsistencies at HOFs. Calculation of permissible abstraction levels involves the addition of permissible takes below each critical point. For example, the standards for Chalk streams are

< Q99 5%, < Q95 10% > Q95 20%

51 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

thus permissible abstraction at Q90 would be: 5% Q99 + 10% (Q95 - Q99) + 20% (Q90 - Q95).

Table 19 Summary of expert standards defined for fish

Restrictive (1) abstraction For Chalk streams (A2) < Q99 5%, < Q95 10% flow > Q95 20% management For eurytopic/limnophylic fish (A1) HOF of Q98. Above HOF 20% abstraction May-June; 50% abstraction July-April. For rheophilic cyprinids (B/C/D) Feb – Jun HOF of Q90, 50% abstraction of flow above HOF. Jul –Jan < Q90 25%

Active flow (2) floods No significant impoundments on Chalk streams management (A2) or lowland rivers with eurytopic/limnophylic (GEP only - fish (A1) see restrictive For rheophilic cyprinids; a large flood (bankfull) management November – January standards for For adult salmon (B/C/D) 3 freshets September – GES) November. For salmonid spawning/nursery areas (B/C/D) 3 small and 1 large flood (Q2) during October – April period (3) No significant impoundments on Chalk streams compensation (A2) or lowland rivers with eurytopic/limnophylic flow fish (A1) For rheophilic cyprinids: Q70 during May - July; Q95 August - April. For adult salmon: Q90 during December – April; Q95 May - November. For salmonid spawning/nursery areas (B/C/D): May –September Q95 during May – September, Q90 October – April.

3.7 Physical character

A project is currently underway, jointly funded by the Centre for Ecology and Hydrology and the Environment Agency, entitled Rapid Assessment of Physical Habitat Sensitivity to Abstraction (RAPHSA). The RAPHSA database contains 65 river sites at which detailed hydraulic data have been collected to undertaken habitat modelling studies, such as PHABSIM. These hydraulic data can be used to study the impact of flow changes on the physical character of river channels. As part of the RAPHSA project, each site was analysed to identify thresholds of change in hydraulic parameters with flow. Figure 24 shows 2 examples of the relationship between average width (for 7 or so cross sections at the site) and flow. Figure 24a shows the River Kennet at Axford, which exhibits a significant reduction in channel

52 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

width as flows drop between Q95. Figure 24b shows that for the Wissey at Langford the significant break point in the relationship is around Q85.

a b

Site 53 Site 212

14 12 11 13 10 9

12 Width (m) 8 Width (m) 7 11 6 100 90 80 70 60 50 40 30 20 10 0 100 90 80 70 60 50 40 30 20 10 0 Flow Percentile Flow percentile

Figure 24 Relationships between flow and average cross-section width at two sites within the RAPHSA database

Each of the 65 RAPHSA sites was analysed to identify break points in these relationships. At many sites the relationship took the form of a smooth curve with no obvious break point. However, threshold points were identified at 36 sites. The range of break points is shown in Figure 25. It can be seen that the model value is around Q95 with a mean of Q92. No obvious relationship was found between threshold level and river site type.

16 14 12 10 8 6 4 number of sites 2 0 84 86 88 90 92 94 96 98 threshold percentile

Figure 25 Distribution of threshold in the relationship between flow and width at RAPHSA sites

This analysis suggests that Q95 marks a significant point where below which conditions in the river change rapidly and hence the river is more sensitive to flow

53 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

change. This provides justification for hands-off flows at Q95 in restrictive management and maintaining Q95 in active management.

Future work in the RAPHSA project will examine these break points at individual cross-sections within each site to assess the variability along river reaches.

3.8 Comparing standards for biotic and a-biotic elements

Sections 3.4 – 3.6 defined expert standards individually for macrophytes, macro- invertebrates and fish. These standards are summarised in Table 20 for comparison. It can be seen that standards for macrophytes and invertebrates are in broad agreement with the only exception being less stringent standards for invertebrates for A1 rivers. All experts felt strongly that protection of the natural low flow regime was very important; they argued forcefully for hands-off flows around Q95). In addition, these two sets of standards vary very little between river types; either 10 or 20%. The experts clearly believe that invertebrate communities in different rivers have different sensitivity to flow change. Such differentiation was not found in the LIFE score analysis, but may be an attribute of the parameters used in the modelling.

54 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

Table 20 Comparing expert standards for macrophytes, invertebrates and fish

Macrophytes Invertebrates Fish

% Period % Period % > Q95 Period A1 10 Mar – May 30 All year 50 Jul – Apr HOF Q98 20 Jun – Feb 20 May - Jun HOF Q98 A2 10 Mar – May 10 All year 20 >Q95 All year 20 Jun – Feb 10 Q90 HOF Q99 25

20 Jun – Feb Adult salmonids D1 10 Mar – May 20 All year All year 20 Jun - Feb 50 HOF Q95 D2 10 Mar – May 10 All year 20 Jun– Feb Salmonid spawning 20 and nursery May–Sep HOF Q95 20 Oct-Apr HOF Q80

Hands-Off flow is Q95 Hands-off flow March – May Q97 All year

The comparison with fish standards is slightly more complex, for two reasons. First, the fish community types do not map directly to the 8-fold classification (A1 – D2). Chalk rivers appear in both typologies (A2) and eurytopic/limnophylic fish relate broadly to A1 rivers. However, rheophilic cyprinids could occur in types B1, B2, C1 and C2 whilst salmonids may occur in any river B1-D2.

A further research project is required to define which communities occur in which river water bodies; for example which water bodies would support spawning salmonids and nursery areas. This research could use tree models as in Figure 13 to define fish communities from physical characteristics of river water bodies and their catchments. Fish community data are held by University of Hull (Cowx et al, 2002).

The second difficulty arises because the experts defined standards in different ways for fish than for macrophytes and invertebrates. The fish experts provided standards in terms of % abstraction of flow left when Q95 has been protected i.e. % of residual flow (actual flow - Q95). Figure 26 shows an example flow regime; for flows above Q82, 50% of flow above Q95 (actual flow - Q95) allows more abstraction than 10% of total flow; between Q82 and Q95 the opposite is true.

Overall it can be concluded that the fish standards are less stringent than those for invertebrates and macrophytes at higher flows (above Q82 in the example) but more stringent near to Q95. For eurytopic/limnophylic fish (which relate broadly to A1

55 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 rivers), for rheophilic cyprinids and for adult salmonids.

A B

2.000 0.160

1.600 0.140

1.200

0.120 0.800

0.400 0.100

0.000 0.080 70.00 75.00 80.00 85.00 90.00 95.00 100.00 Percentile of time exceeded 01/01/86 01/02/86 01/03/86 01/04/86 01/05/86 01/06/86 01/07/86 01/08/86 01/09/86 01/10/86 01/11/86 01/12/86

Figure 26 Comparison of natural flow (blue), flow with abstraction of 50% of flow exceeding Q95 (red) and 10% of total flow (green) both with a HOF of Q95. a. hydrograph; b. low flow duration curve.

Table 21 gives the proportion of Q95 that can be licensed under the RAM framework of CAMS (Environment Agency, 2002). It can be seen that at Q95, values given by experts for GES are equivalent to moderate to low sensitivity. A major difference is that the RAM framework permits abstraction below Q95 whereas for GES no abstraction is permitted below Q95.

Table 21 Abstraction standards from RAM framework (Environment Agency, 2002)

Abstraction flow Very high High Moderate Low Very low sensitivity band % of Q that can 95 1 – 5 5 -10 10 – 15 15 - 25 25 - 30 be abstracted

It should be noted that the experts felt that good ecological status may not be achieved by making compensation flows (i.e. long periods of constant flow) from impoundments, so active management standards are probably only appropriate for good ecological potential (GEP).

The LIFE score analysis suggested that there if regulation is based on low flow statistics, such as Q95, then sensitivity to flow change is not significant between types. However, data available for the analysis did not cover the more upland types. Hence we recommend that the expert consensus should be given highest priority. Nevertheless, the experts did not suggest widely differing standards for different rivers.

The use of Q95 as a critical flow point at which sensitivity to flow alteration changes, is supported by analysis of physical river structure from the RAPHSA database.

Table 22 shows the generic river thresholds (standards) proposed by English Nature for designated rivers (SSSI, SAC). These are examples of river water bodies that

56 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 should be maintained at high ecological status (HES). It can be seen that the standards are in the range 10% reduction from natural flow for sensitive rivers (with 1-5 % below Q95) which is the same as the experts view for rivers of type A2, C2, D2. For rivers of very low sensitivity (in which category A1 river water bodies would be place), reduction levels are 20% (with 1-5 % below Q95).

Table 22 Generic river flow thresholds for designated rivers from English Nature

RAM Maximum % reduction from Environmental Weighting band daily naturalised flow

(sensitivity) flow >Qn50 flow

Very High 10 10 1-5

High 15 10 5-10

Moderate 20 15 10-15

Low N/A N/A N/A

Very Low 20 20 15

57 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

4. RIVER WATER BODY RECOMMENDED STANDARDS

4.1 Identifying the type of river water body

In the project workshops, macrophyte and macro-invertebrate experts endorsed the generic 8 type classification of river water bodies based on Holmes et al. (1998). After the workshops, the analysis of specific studies, such as the Rivers Itchen (Halcrow, 2004) and Wylye (Dunbar et al, 2000), suggested that Chalk rivers should be further divided into two types, since the headwaters and downstream areas exhibited different sensitivities to flow alteration. A threshold drainage area of 100 km2 was adopted as the division between the sub-types.

Fish experts recommended an alternative fish-specific typology based on Cowx et al (2004). Two of the fish types were equivalent to two of the generic types (A1 with eurytopic/limnophylic fish and A2 with Chalk stream fish). Expert standards for macrophytes and macro-invertebrates were broadly equal to or more stringent those for reheophillic cyprinids and adult salmon (Table 20) so separate types for these were not needed. The fish standards were more severe only for salmonid spawning and nursery areas. The Project Team thus concluded that standards were required for 10 river water body types; the 8 generic types with a sub-division of A2 (A1, A2(hw), A2(ds), B1, B2, C1, C2, D1, D2) plus salmonid spawning and nursery areas.

Table 23 Recommended method for classifying river water body types

river water body type at site biological data catchment data

A1 / eurytopic/limnophylic macrophyte or fish data tree model fish A2 / Chalk river fish subtype hw – headwater macrophyte of fish data tree model subtype ds – downstream B1 macrophyte data tree model B2 macrophyte data tree model C1 macrophyte data no method C2 macrophyte data tree model D1 macrophyte data Geographical location D2 macrophyte data tree model salmonid spawning and fish data no method nursery areas

Where local macrophytes surveys have been undertaken, such as at those sites in the JNCC database, generic river types can be identified from these data. Likewise, water bodies with known salmonid spawning and nursery areas could be classified as such. It is important to note that many water bodies in the UK have been altered to some extent by, for example weirs, sluices, dredging, straightening, pollution, loss of shading, even if they have not been formally classified as heavily modified water bodies. In such cases, observed riverine communities may be improverished

58 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 versions of the natural community for the water body type. Where the communities are significantly different from natural, local fish, invertebrate or macrophyte data should not be used to define the water type, since this may lead to use of standards that permit abstraction that would preclude natural sensitive species from returning if other conditions are ameliorated.

For other sites, in the UK the tree-based model in Figure 27 provides a method for identifying the generic river water body types A1, A2, B1, B2, C2 and D2 from catchment data (Table 23). Type D1 river water body can be identified by geographical location (mainly the New Forest, Scottish Flow Country and Western Isles). The model does not distinguish type C1, so this type will only be identified where a macrophyte survey has been undertaken. There is currently no method for identifying salmonid spawning and nursery areas based on catchment data.

SAAR<| 810.5

BFIHOST< 0.715 BFIHOST>=0.3615 AREA>=251.8 A1 A1 A2

SAAR< 1413 D2

BFIHOST>=0.7495 AREA>=32.33 AREA>=267.4 A2 C2 D2 SAAR< 1155 B2 B1 C2

sub-type A2 (hw) AREA<100.0 sub-type A2 (ds) AREA>=100.0

Figure 27 Recommended tree-based model for 6 river types (left branch = yes; right branch = no to the logical test stated at the top of the branch)

59 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

Figure 28 River water body types in North England and Southern Scotland predicted by the tree model in Figure 27

60 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

Figure 29 River water body types in south Wales and south west England predicted by the tree model in Figure 27

61 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

Figure 28 shows a map of rivers in northern England and southern Scotland together with the locations of macrophyte sample sites used to develop the recommended river typology. The sites are colour coded according to the river water body type predicted by the tree model in Figure 27. It can be seen, for example, that the headwaters of most rivers are classed as D1 becoming C2 downstream. The middle reaches are predominantly B2, particularly the Tweed.

Figure 29 shows a similar map to Figure 28, this time for south Wales and south west England.

A fish atlas has been published by CEH which shows the locations where different fish species have been recorded in Great Britain (Davis, 2004). Figure 30 shows records of Atlantic salmon (Salmo salar) within 10 km squares. However, the atlas does not provide maps of the spawning or nursery areas that could be used to locate this river water body type. Local knowledge of salmonid spawning and nursery areas provides the only method currently available.

Figure 30 Locations in Great Britain where Atlantic salmon have been recorded (see http://www.searchnbn.net/gridMap/gridMap.jsp?allDs=1&srchSpKey=NBNSYS0000188606)

4.2 Standards for river water body types

In this step the expert advice from the project workshops was taken to define recommended environmental standards for UK agencies for restrictive flow management (abstraction). To achieve this, the following principles were adopted:

62 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

• Standards should be based on variations in flow from the natural hydrological regime of the river water body, signified as Qn. In exceptional circumstance an alternative baseline can be considered, such as where the flow regime has been altered significantly for many years so that the ecosystem has become adjusted and using the natural regime as the baseline would cause ecological degradation. An example of this could be the River Don, where at low flows more than half the flow may be contributed by discharges. In this case the historical gauged flow may be considered as the baseline. • Standards should be based on the expert views as expressed at the project workshops. They identified protection of low flows as a key element in achieving GES, with Qn95 representing a critical threshold below which abstraction should be significantly reduced or stopped. • Standards should vary between the river water body types to reflect the expert views of their sensitivity to flow change. However, expert views suggested that, in some cases, within the same river water body type different standards were appropriate for macrophytes, invertebrates and fish. It was considered that these needed to be combined into a single standard for each type; normally by taking the most stringent standard. • Standards should vary with time of year. For example, March to May represents a critical time for river macrophytes and more stringent standards are required for this period than for June to February. Spawning time for fish and development of juveniles (May to June for cyprinids, October to April for salmonids) is the most critical time and more stringent standards are required for these periods. • In defining critical flow statistics, e.g. Q95, annual flow data should be used. This provides added protection to naturally low flow periods i.e. seasonal Q95 would be lower than annual Q95 during, for example, late summer. Clearly this approach gives less protection to period of low flows that occur during normally high flow periods.

number of rivers

0 5 10 15 20 25 standard to achieve GES

Figure 31 Histogram of maximum abstraction that can achieve GES for a set of rivers (blue curve), the standard that ensures all rivers achieve GES (purple line) and the risk-based standard that ensures GES will be achieved most of the time (yellow line)

63 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

• The Project Steering Group dictated that standards must follow a risk-based approach as adopted by UK regulatory agencies. It was taken that the standards recommended by the experts were those which ensure that all water bodies would achieve GES. In the risk-based approach slightly less stringent standards can be used if it is accepted that their application may lead in some cases to a river water body failing good status. Consequently, granting of abstraction licences must be associated with monitoring so that the status of the water bodies can be assessed and the conditions of the licence altered, if appropriate. This idea is show hypothetically in Figure 31, where the blue line represents a histogram of the distribution of actual maximum permissible abstractions rates for a range of rivers required to achieve GES. If the standard is set at 0% (no abstraction), all rivers achieve GES, if the standard is set at 5% most rivers achieve GES, but some fail. Unfortunately there are no data with which to define the precise form of Figure 31, the different between the risk- based standards and those of the experts remains subjective.

Table 23 Recommended standards for UK river types for achieving GES given as % allowable abstraction of natural flow (thresholds are for annual flow statistics)

Type Season flow > Qn60 Flow > Qn70 flow > Qn95 flow < Qn95

Apr – Oct 30 25 20 15 A1

Nov – Mar 35 30 25 20

Apr – Oct 25 20 15 10 A2 (ds), B1, B2, C1, D1 Nov – Mar 30 25 20 15

Apr – Oct 20 15 10 7.5 A2 (hw), C2, D2 Nov – Mar 25 20 15 10

Salmonid spawning Jun – Sep 25 20 15 10 & nursery areas (not Chalk flow > Q flow < Q Oct – May 20 15 80 80 rivers) 10 7.5

64 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

• The experts advocated that an absolute hands-off flow (HOF) restriction should be applied in many cases, with no abstraction below the threshold. It was the view of the Project Steering Group that alterations to the flow regime of the order of 5-10% were at the margin of hydrological measurement error and unlikely to have a significant impact on GES. Permitting 5-10% abstraction below the threshold would allow flexibility in applying the standards to water users with modest, but constant abstraction needs. • Higher abstraction may be permitted at higher flows, above Qn70 and Qn60. • Standards for achieving moderate ecological status (MES) will be less stringent than for GES, of the order of 10% more permissible abstraction. In turn standards for achieving poor ecological status permit an additional 10% abstraction. • A threshold level for the alteration of river hydraulics from natural needs to be set beyond which the general standards are not appropriate and site investigations are required. • The English Nature 10% standard is set to maintain or restored favourable conservation status in Habitats Directive and other designated sites. The relationship with GES and HES needs to be noted.

Table 23 provides standards for UK river types for achieving good ecological status (GES) developed by the project team, following direction from the Project Steering Group to take a risk-based approach with the agencies undertaking monitoring at sites where the standards are applied to catch any that fail GES. As insufficient knowledge was available to define the form of the graph in Figure 31, i.e. how many rivers might fail GES by employing these standards to Table 23, is recognised as the project team’s expert experience. These standards are given in the form of the allowable abstraction as a percentage of the natural flow on any day. It assumes that Qn95 is a critical flow below which more stringent standards are required (or Qn80 in the case of salmonid spawning and nursery areas). All critical flows (e.g. Qn95) are specified in terms of the annual flow duration. In addition, standards are more stringent for the period March to June (covering macrophyte reproduction and cyprinid spawning) for generic types A1 to D2. For salmonid spawning and nursery areas the critical period is October to April.

Table 24 Recommended standards for UK river types for achieving HES given as % allowable abstraction or discharge related to natural flow (thresholds are for annual flow statistics)

Type Season flow > Qn95 flow < Qn95

all river types all seasons 10 5

Table 24 provides standards for UK river water body types for achieving high ecological status (HES). These are based on the Project Team’s views of increased protection on the standards for GES. In setting these standards, only hydro- morphological conditions are considered and flows should be neither reduced by abstraction nor increased by discharges by more than the critical values given. In

65 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 addition, the standards relate to gross alterations of the regime, not a net balance between abstraction and discharge i.e. HES would not be achieve where significant abstraction takes place even if abstracted water is returned to the river in the same quantity and quality. The standards were developed independently of the thresholds for designated rivers by English Nature (Table 22), but fall within the range of Very High and High sensitivity.

Table 25 Recommended standards for UK river types for achieving MES given as % allowable abstraction of natural flow (thresholds are for annual flow statistics)

Type Season Flow > Qn60 flow > Qn70 flow > Qn95 flow < Qn95

Apr – Oct 40 35 30 25 A1

Nov – Mar 45 40 35 30

Apr – Oct 35 30 25 20 A2 (ds), B1, B2, C1, D1 Nov – Mar 40 35 30 25

Apr – Oct 30 25 20 15 A2 (hw), C2, D2 Nov – Mar 35 30 25 20

Salmonid spawning Jun – Sep 35 30 25 20 & nursery areas (not Chalk flow > Q Flow < Q Oct – May 30 25 80 80 rivers) 20 15

Table 25 provides standards for UK river water body types for achieving moderate ecological status (MES) defined by the Project Team. These are given as the allowable abstraction as a percentage of the natural flow on any day. In the absence of ecological data to support a quantitative scientific analysis, these figures were derived by the Project Team using their judgement that MES was likely to be achieved in general with further reductions in flow of 10% from GES. River water bodies where abstraction greater than the standards for MES will only achieve Poor Ecological Status (PES).

Each of the above standards (GES Table 23; HES Table 24; MES Table 25) apply to river water bodies in which the hydraulic properties are not significantly altered from natural, for example by a major weir. “Significantly altered” here is defined as having

66 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 an RHS modification score > 1496. In the RHS, such rivers are referred to as heavily modified, but this should be confused with the WFD HMWB classification. It is noteworthy that the definition of potential HMWBs under WFD is undertaken partly using RHS modification scores. Thus water bodies in the RHS heavily modified class may eventually be classed as HMWB and would thus fall outside the scope of the standards, and would need to achieve GEP. However, designation of a water body officially as HMWB is based on economic criteria; i.e. whether the modifications perform an economically important function. In theory, if the water body is not designated as HMWB, then the modifications may eventually be removed, thus the standards would be applicable.

4.3 Applying the river water body standards to licensing

Three characteristics of the environmental standards are noteworthy when considering their application to licensing: 1. the allowance percentage relates to flow at the time of abstraction, i.e. it can change continually 2. the allowances have hands-off flows at, for example, Qn95 3. the allowances vary seasonally in some cases.

Application of these variations directly in a licence implies two things: 1. the licensee knows what the flow is on that day 2. the licensee can operate with different levels of abstraction at different times.

Water abstraction is essential to human life both directly for drinking and indirectly for growing food, power generation industrial processing and other uses. In managing water resources, UK regulatory agencies have a duty to balance the needs of the abstractor, the impact of the abstraction on the environment and the rights of other users. Some users, such as large water companies or canal owners, own storage reservoirs which provide flexibility; so that they could abstract more water during high flows and store this in the reservoir for use when less water is available during low flows. In addition, water companies may have licences for conjunctive use of surface and groundwater which also provides flexibility. In such cases, they may be able to manage with different abstraction allowances at different times. In addition, for major abstractions there may be a river flow gauging station near-by that can be used to define the allowance at any time. However, the agencies recognise that many water users (from fish farm owners to power station managers) need to be able to abstract a constant volume of water and they may be abstracting from a river water body where no flow gauging is undertaken. Thus, they may not be able cope operationally with a changing abstraction allowance and have no way of calculating the actual flow in the river. In these cases, simplified standards will be required to provide the licensees with appropriate water allowances.

One way of approaching the setting of single unvarying abstraction licenses is to consider the impact on flows at various frequency of occurrence. For example, if an abstraction allowance of 10% of Qn95 is set, the implications for flows at Qn99 need to be considered and the risk of failing the Qn99 standard assessed. This is illustrated in Figure 32 which shows for catchments in England and Wales, 10% of Qn95 as a percentage of Qn99. Type D2 is not well represented in England and Wales, so data for the entire UK may show slightly different patterns. It is evident that for most catchments, 10% of Qn95 is, on average, equivalent to around 15 % of Qn99. In exceptional circumstances, the river would be dry under such circumstances (i.e. where 10% of Qn95 is greater than or equal to 100% of Qn99). Research used to develop Low Flows 2000 found that the steepness of the flow duration curve (and hence the ratio of Qn99 to Qn95) is related to BFI. This is consistent with Figure 32,

67 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

which shows that for Chalk rivers (high BFI - flatter flow duration curves) 10% of Qn95 is la lower % (around 13%) of Qn99. Figure 32 also shows that this % value varies more within than between river water body types. Hence, we recommend that both Qn99 to Qn95 are calculated when setting licences, if the licensed amount is a fixed proportion of Qn95, so that implications of the abstraction at Qn99 can be assessed.

In November 2005, a final workshop was held to report the draft standards to experts. The experts felt that it was not possible to specify a constant volume that could be abstracted at any flow and still achieve GES, except by defining the volume as a percentage of the very lowest flow. It was suggested that if a licence was granted for constant abstraction at any flow, then the abstraction should not reduce flow at Qn99 by more than 25%.

Figure 30 Box plot showing, for catchments in England and Wales, 10% of Qn95 as a percentage of Qn99

One of the challenges of this WFD 48 project has been to satisfy both the broad requirements of the Water Framework Directive and practicalities of licensing water abstraction. The WFD requires the definition of thresholds to meet specific levels of ecological status. The WFD48 Project did not require any compromise between achieving ecological status and meeting water users’ needs; as this balance is made by the UK regulatory agencies in deciding how to apply the environmental standards to regulation. At the expert workshop, the specialists highlighted they had had insufficient experience in setting standards; they were called upon at short notice to provide input within a few hours of workshop, then largely not contacted until a similar workshop several years later. The South African experience appeared to be one of more continuous interaction between scientists and implementing agencies with expert involvement in defining environmental flows in real case studies. This has built mutual understanding and led to better integration of research results and

68 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3 applications. We recommend that UK agencies develop better, longer-term and more consistent collaboration with UK scientists.

The standards can only be applied to river water bodies down to their tidal limit. Although flows to estuaries were mentioned in the fish workshop with regard to salmon migration, this topic was outside of the scope of the project. Nevertheless, flows to estuaries are an important element of environmental flows; even though estuaries and near-shore zones are saline, their ecosystems rely on freshwater inputs. This topic needs to be the subject of a separate research project.

Through this report standards have been related to the natural flow regime (Qn). However, it is recognise that the most appropriate baseline may be the gauged flow, and not the natural flow.

4.4 Heavily modified water bodies (HMWBs) and good ecological potential (GEP)

The WFD allows limited exceptions to achieving Good Ecological Status. In particular, certain water bodies will be required to achieve an alternate objective of at least "Good Ecological Potential". This objective takes account of the constraints imposed by physical modifications to the water body and is equivalent to achieving Good Ecological Status in unmodified water bodies. Such designation will either be as “Artificial” or “Heavily Modified” as appropriate, and will depend on the results of the two designation tests outlined in Section 4.3 of the WFD.

It is unclear whether hydrological modification alone would be grounds for designation as a heavily modified water body (HMWB), indeed there are conflicting views. On the one hand, there is some interpretation in the Common Implementation Strategy for the WFD that suggests that this is true, and it is thought that some countries which generate significant amounts of hydropower, such as Austria and Norway, are arguing for this. On the other hand, in the project “Guidelines for the Identification and Designation of Heavily Modified Water Bodies in England and Wales” (Dunbar et al. 2002) led by CEH was specifically asked to concentrate on morphological modifications rather than hydrological. In addition, some have the view that both hydrology/hydraulics and morphology need to be altered for HMWB to be applicable (Martin Mardsen, pers. comm.). Bearing the above in mind, rivers whose flow regime is heavily regulated will likely have non-natural morphologies because of this, so the debate could in part be superfluous. However, there could also be unclear borderline cases where morphology is not altered, but where the flow regulation is delivering significant economic benefit.

Whilst HMWBs are strictly outside of the scope of this project (i.e. the project was not required to define standards for HMWBs) the issues of HMWB and GEP were discussed at the expert workshops (see Annex 2, section 4), so it seems pertinent to summarise the outcomes here. The experts recognised that dams and other infrastructure may alter significantly the hydrological regimes of downstream water bodies but those water bodies may not themselves to designated as HMWB. The following general principles were concluded by the experts

1. the conventional mode of operating dams, with constant releases (compensations flows) for long periods would not achieve GES. Natural hydrological variability is an important element for maintaining healthy freshwater ecosystems 2. It does not make scientific sense to define two different sets of standards that can achieve GES i.e. one for abstractions and one for releases from

69 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

impoundments. To achieve GES below impoundments (active flow management), standards defined for abstraction (restrictive flow management) would need to be applied; i.e. whilst the whole flow regime may be reduced, natural variability should be maintained. 3. to achieve GEP, some basic elements of the natural regime need to be maintained, even if variability is not. In particular, floods competent to move gravel and stimulate migration are required at key times of the year and occasional larger floods to maintain channel form. 4. constant flow releases (compensation flows) need to be altered during the year for fish and for some macrophytes, releases should fluctuate around Q95 by +100 / -50% to maintain inundation/drying of bryophytes.

Table 26 Summary of expert views for achieving GEP in river water bodies downstream of impoundments

Floods Compensation flows macrophytes Invertebrates Fish macrophytes invertebrates Fish A1 20-30% 40% natural Qn90 natural floods floods 5-7 x A2 Qn50 80% natural Qn80 floods

B1 As A1/A2 60% natural Rheophilic Qn95 Qn70 Rheophilic plus freshet floods cyprinids: cyprinids: 5 x Qn95 May-July no May-July B2 Mar-May major floods Qn70 July – Jan July – Jan bank-full Qn70 C1 70% natural flood floods Adult Adult salmonids: C2 As A1/A2 60% natural salmonids: fluctuations Dec-Apr plus freshet floods Sep-Nov around Qn95 Qn90 Qn50 Mar- 3 small May-Nov D1 May 80% natural freshets Qn80 Qn95 floods Salmonid Salmonid D2 50% natural spawning: Qn60 spawning: floods Oct-Apr 3 Oct-Apr small floods Qn90 to clean May-Sep gravel and Qn95 migrate adults; 1 large flood Qn2

Table 26 provides a summary of the experts’ views for achieving GEP in river water bodies. It can be seen that the experts felt that invertebrates in particular require a flooding regime close to natural. More work would be required to turn these views into standards for achieving since they represent broad-brush opinion of the experts within a project that was not focusing on HMWBs.

70 SNIFFER WFD48 Development of Environmental Standards (Water Resources) Stage 3

4.5 Expert feedback workshop

An addition workshop was held on 21 November 2005 to provide feedback on the recommended environmental standards to the experts that had been involved in the initial standard setting. Standards were sent to all invitees prior to the workshop. Unfortunately, many of the experts were unable to attend due to prior commitments. The report of the workshop is presented as Annex 4.

A major point of discussion was that for practical implementation, standards would be best presented as a constant quantity of water available for abstraction as a % of Q95 at the site. The experts argued that river ecosystems could only be protected by defining abstraction as a % of flow on the day. As a compromise, it was suggested that a rule of thumb should be that no abstraction greater than 25% of Q95 should be permitted.

Only minor suggestions were made for changes to the environmental standards (Tables 23, 24, 25). The seasons were re-defined to Nov-Mar and Apr-Oct. The standards for A1 rivers could be made less restrictive due to their low sensitivity to flow change.

Additional comments were received following the workshop. These comments included: • Rheophilic cyprinids will not occur in type D1, D2. • WFD 48 takes little account of importance of migration flows in summer for e.g. sea trout. • More use could be made in future of RHS – enhanced version – which takes into account the geometry and substratum of the channel. • Some fish experts questioned whether macrophytes and invertebrates are more sensitive to flow variation than fish.

• Any decision to replace HoFs with allowable abstraction below Q95 (the risk- based approach) is a political decision, not an ecological one. The onus of proof of lack of likelihood of ecological damage should fall on the abstractor rather than the regulator. • In rivers that are currently impacted (pollution, weirs) and have no flow-sensitive species, a greater take is allowed, therefore the river will be kept in poor status.

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